The present invention relates generally to the data processing field, and more particularly, relates to a method and apparatus for implementing an in-situ digital harmonic computation facility for direct access storage device (DASD).
Computers often include auxiliary memory storage units having media on which data can be written and from which data can be read for later use. Disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks.
Data located on a particular track on a disk surface is read or written by properly positioning a data transducer head directly over the track. In order to maintain the head in proper position over the data track, track-following servo systems often are incorporated into disk drives. Servo position control is used to position the data heads in registration with the data information tracks. A sector servo system uses the data heads as servo transducers in a time-multiplexed fashion. As a head is following a particular track on a rotating disk, the head will pick up data information and servo information alternately. Servo information, interlaced with data information, is prewritten on the disk surfaces at manufacturing time within narrow radial sectors as spokes on a wagon wheel. A servo system that interlaces data and servo information is commonly referred to as sector servo or embedded servo. Another servo system uses a dedicated servo transducer head to read position signals recorded in servo information tracks on a dedicated disk surface. The data heads are ganged with the servo head for simultaneous movement relative to the data information tracks and the servo information tracks. To access the disk drive unit, a feedback sector servo controlled drive system locates the head in a desired position, where data is to be written or read.
Techniques for detecting disk surface defects are known. Most commercially available disk drives store a standard primary defect list (P-list) and a grown defect list (G-list) in a protected area of the disk drive, often referred to as disk defect logs. The P-list is generated for each disk file at manufacturing time and stores information of specific locations of magnetic surface defect sites and the alternate site for storing data. The G-list is generated and periodically updated while the disk drive is in use including stored information of grown defects that occurred after manufacturing. Special manufacturing slider-glide-test procedures, such as Harmonic Ratio Flyheight (HRF) typically are used to estimate flying height and Clearance Modulation Detection (CMD) typically used to detect the presence of raised disk asperities in direct access storage device (DASD). Currently many direct access storage devices (DASDs) include a General Error Measurement (GEM) facility for error detection.
It is desirable to provide an improved method and apparatus for detection of error and critical conditions in a DASD. It is desirable to provide a simpler and more computationally efficient method to perform functions than presently executed in the GEM facility.
A principal object of the present invention is to provide a method and apparatus for implementing an in-situ digital harmonic computation facility for direct access storage device (DASD). Other important objects of the present invention are to provide such method and apparatus for implementing an in-situ digital harmonic computation facility for direct access storage device (DASD) substantially without negative effect; and that overcome many of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for implementing an in-situ digital harmonic computation facility for direct access storage device (DASD). A digital sequence output of a DASD channel from a constant write frequency field on a disk surface is applied to a plurality of adders for modulo-n summing the digital sequence. A harmonics computation block provides discrete Fourier transform computing based upon the modulo-n summed digital sequence to produce a plurality of harmonic coefficients. A plurality of estimate functions utilize predetermined ones of the plurality of harmonic coefficients for estimation of predefined conditions in the DASD.
In accordance with features of the invention, the plurality of estimate functions include a flyheight estimate function, a readback signal asymmetry estimate function and a thermal activity estimate function.